In five words, Len Brown's deputy Penny Hulse captured his six years as the first mayor of the amalgamated Auckland.

Mr Brown leaves the office with a legacy that will not be fully appreciated until the 2023 opening of the City Rail Link project which he championed.

The 3.4km twin-rail tunnels will cost around $3 billion, and took Mr Brown nearly three years to help convince the government to move from public scorn, in 2010, to Prime Ministerial agreement, in 2012, to co-fund the project.

The tunnels will create a loop under the CBD, boosting the frequency and capacity of the rail network, and are expected to trigger large commercial property developments along its route.

Work has begun, and completion will be testament to Mr Brown's commitment to making a change as transformative as the amalgamation of Auckland's eight local bodies, which brought him to office in 2010.

A welder working on the City Rail Link project. Photo: RNZ / Claire Eastham-Farrelly

Also on the 'done' list for Mr Brown's two terms was co-shepherding the biggest planning exercise undertaken in this country, the Unitary Plan which will bring higher density housing to more of the city.

Another milestone yet to be fully tested is the agreement with the government on the direction and funding of major transport projects in coming decades - again an unprecedented step in long-term city development.

Brown's second-term support slumped

But Mr Brown's incumbency also had a flipside which tainted his second term in office, and ultimately made him unelectable in 2016.

Protesters pursued Mr Brown outside the Town Hall, waving placards, heckling him and demanding that he resign. Photo: RNZ

The episode cost the mayor significant public support, and during the second-term, councillors once loyal turned privately hostile.

Ms Hulse, in her tribute speech, noted that public loyalty to Mr Brown had come at a cost to some councillors.

"Some of those have had to burn off some degree of political support by being seen to politically support you."

Len Brown lost the support of key councillors during his second term, here with deputy mayor Penny Hulse. Photo: RNZ / Todd Niall

Her public support broke in mid-August after Mr Brown unexpectedly voted against dumping affordable housing quotas in the Unitary Plan, after she and council staff found they were unlikely to be effective.

He said he will do some unspecified work with groups in south Auckland, and is interested in working with technology start-ups.

Regardless of public opinion, Mr Brown will always be the first mayor of a united Auckland, and one whose doggedness delivered what might be the most transformative project in the city since the harbour bridge opening in 1959.

Auckland's outgoing mayor Len Brown says he regrets not pushing the government harder to build more houses. He speaks to Todd Niall about his triumphs and regrets running NZ's biggest city. Video, Audio